Dressing mechanism



Oct. 15, 1946. P. F. BARKER ETAL DRESSING MECHANISM Filed July 2e; 1943 10 Sheets-Sheet l t. l5, 194%, P. F. B'ARKER ErAL DRESS ING MECHANI SM Filed July 28, 1943 10 Sheets-Sheet 2 O fm.. 7%

f Tan mventor PAUL fr' BARKE/e, HERBERT G. HnKTMnN CLQRENCE ZGHLLOv/HY BERNARD M. KUNES u i l Gttorneg v P. F. BARKER 'AL.

DRESS ING MECHANISM Ca 10 Sheets-Sheet 3 Filed July 2S, 1943 r'wentot PAUL E EAR/(EB, HERBERT G. #HRT/*MN Oct. l5, 1946. P. F. BARKER ETAI. 2,409,240

DRESSING MECHANISM Filed July 28, 1943 10 Sheets-Sheet 4 Imventor Paul. f. BAKKER, HERBERT 6. #mer/MN v CLARENCE T. GHLLOWHY d, JEBNARD M KUNES Gttorneg Oct. 15, 1946. P. r.y BARKER ErAL DRESSING MECHANISM Filed July 28, 1943 10 Sheets-Sheet 5 mmm mm". m m. .r...- N m. mmm HA Tf ze, ...a HlI BY l um 4 L f @Z ...M L... el ma Pa E, ie. s wf a am Mt. n

l Oct. l5, 1946.

P. F. BARKER ErAl.-

DRESSING MECHANISM Filed July 28, 1943 10 Sheets-Sheet 7 Oct. 15,v 1946. P. F.. BARKl-:R ETAL 2,409,240

DRESSING MECHANISM Filed July 28, 1943 1o sheets-'sheet s l A A zza ia/f,

2,55 n Z50 q 250 Fdn Z7 Zswentor Pau; E emerse, fis/esser c. Haz mmv aneth/E 7.' GnuowAY a BERN/go MKV/ves t. E5, 1946. P. F. BARKER ErAL- 2,409,240

DRESSING MECHANISM Filed July 2s, 1943 1o` sheets-sheet 9 2&7 265 Snnentor cmu-Nc: z @mow/w a emmen Mk1/Nes PAUL F. EHR/YER, HERBERT GJ/HKTMHN Oct 15, 1946..

P. F. BARKER ETAL DRESSING MECHANISM med July 2a, 194s 1o sheets-Sheet 1o nnentor Pl PAUL f: BHRKE, HERBERT G. HHRT'MHN CLHRENCE GHLLOWHY 8 BEKNHKD M KUIYES /1 Gtorneg Patented Oct. 15, 1946 'iss erst orgie DRESSING MECHANISM Application July 28, 1943, Serial No. 496,452

(Cl. 12S-11) 30 Claims.

The present invention relates to methods and to mechanisms for dressing grinding wheels and particularly to a method and mechanism for dressing wheels that are to be used for grinding gears. In a more speciic aspect, the invention relates to methods and apparatus for dressing rotary annular grinding Wheels such as are employed in the generating-grinding of spiral bevel and hypoid gears.

In conventional generating-type spiral bevel and hypoid gear-grinders, the grinding Wheel is mounted on an oscillatory cradle that is rotated in time with the rotation of the work to produce the generating motion. To grind gears of different spiral angles, the Wheel has to be adjusted on the cradle angularly about the cradle axis, and the wheel-dressing mechanism ls mounted to be adjustable with the Wheel so as to be in operative relation with the wheel in any position of angular adjustment of the wheel. The dressing mechanism is usually mounted to be adjustable around the periphery of the Wheel to position it as far as possible away from the work, but even so diiculty has been experienced on some jobs in obtaining sufficient clearance between the dressing mechanism and the Work or its support during grinding. This has limited the capacity of the grinders despite the fact that otherwise the machines might be capable of handling a greater range of Work.

The dressing mechanism itself consists ordinarily of a pair of side dressers for dressing the inside and outside surfaces of the wheel, respectively, and of a tip dresser for dressing vthe tip surface of the Wheel and the rounds at the junctures of the side surfaces With the tip. In dressing, a diamond, or other hard surfaced tool, is moved across the wheel surface to be dressed while the Wheel is rotated on its axis at high speed, usually at the same speed as is employed during grinding. In the dressing operation then, the dressing tool actually turns a helix in the wheel surface being dressed. The lead of this helix, that is, the rate at which the dressing tool is moved across the rotating Wheel, determines the iinish of the dressed surface. The faster the movement of the dressing tool, the coarser the dressed surface. For a fine surface finish, the dressing tool must be moved at a relatively slow rate.

In the machines heretofore built, the side and tip dressers have been operatively connected together either mechanically or hydraulically so that they perform and complete their dressing operations simultaneously; that is, while a side- 2 dressing tool is moving across one side of the grinding Wheel to dress the same, from top to bottom, the other side-dressing tool is moving across the other side of the grinding wheel to dress the same from bottom to top, and the enddressing tool is moving across the tip of the Wheel from one side to the other to dress the tip and to form the desired rounds at the junctures of the sides and the tip. NOW the height of the sides of a wheel is greater than the Width of the tip of a wheel because the height of the sides of the teeth of a gear is greater than the width of the bottom of its tooth spaces and the wheel, of course, has to be commensurate with the gear to be ground, AsV a result in conventional types of dressing mechanisms, the tool for dressing the tip of the wheel moves more slowly than the tools for dressing the sides of the Wheel. Consequently, the tip-dresser dresses a finer surface on the rounds and on the tip of the wheel than the surfaces dressed on the sides of the Wheel by the side dressers.

This is of no consequence in the automotive field, for the bottoms of the tooth spaces of automotive gears and the llets, which join the bottoms with the sides of the tooth spaces, are not ground. In the aeroplane iield, however, gears are heavily loaded, and to eliminate surface cracks which may become points of incipient breakage, the tooth space bottoms and the llets are ground. We have discovered that if the tip and rounds on a Wheel are dressed too ne, the fillets and bottoms of the tooth spaces are likely to be burned when the gears are ground. This is dangerous because a burned surface is a surface already full. of cracks and ripe for breakage under load.

We have discovered another factor, also, that must be taken into consideration in the dressing or annular grinding wheels. We have found that Where an annular grinding wheel is rotated at high speed the wheel tends to expand under centrifugal force and to press the outside surface of the wheel against the longitudinally concave side ci a tooth space being ground thereby with greater pressure than that with which the inside surface of the Wheel engages the convex side of that tooth space. As a result, we have further discovered that if the outside surface of the wheel is dressed to the same fineness as is required on the inside surface of the Wheel, then the outside surface of the Wheel Will burn the work, and again disaster may follow.

One object of the present invention is to provide a dressing mechanism in which the side and end dressers are actuated simultaneously but in which the rates of travel of the side and end dressers can be controlled independently of each other.

Another object of the present invention vir to provide a method and apparatus for dressing grinding wheels in which the tip surface of the wheel and the rounds, which join the tip with the sides, may he dressed simultaneously with the sides but to a finish sufliciently coarse as not to burn the work.

Another object of the invention is to provide a method and apparatus for dressing grinding wheels With which the tip of the wheel may bedressed to a iinish which is no finer than the surfaces dressed on the sides of the wheel.

A further object of the invention is to provide a dressing process and apparatus for dressing annular grinding wheels in which the outside and inside surfaces of the wheel may be dressed to different degrees of nish, the outside surface being dressed to a coarser nish than the inside surface, to compensate for and counteract the eiect of centrifugal force on the wheel in use.

Another object of the invention is to dress the sides and tip of a grinding wheel so that it will grind tooth sides and tooth space bottoms on a gear which will have substantially uniform surface nish.

Still another object of the invention is to dress the sides and tip of a grinding wheel so that the wheel can be used to grind gears faster without danger of burning than they can be ground by conventionally dressed wheels.

A further object of the invention is to provide a dressing mechanism having side and tip dressers in which the dressers may be swung away from the grinding wheel on completion of the dressing operations so as to clear the wheel and permit of grinding any gear within the capacity of the machine on which the dressing mechanism is used without danger of interference oi the dressingr mechanism with the work or its support.

A further object of the invention is to provide a dressing mechanism having separate side and tip dressers in which a single control valve may be employed to control the movements of the side and tip dressers to and from operative position as Well as the operation of these dressers when in operative position.

Another object of the invention is to provide a dressing mechanism in which the mechanism for advancing the wheel in accordance with the amount of stock to be dressed off of the wheel is controlled from the same valve which controle the operations of the dressing mechanism itself.

Another object of the invention is to provide a tip dressing mechanism capable of dressing a straight tip surface on a wheel with rounds at the junctures of the tip with the sides of the wheel in a single continuous movement and which will be simpler and cheaper than tipdressing mechanisms of this character heretofore employed.

A further object of the invention is to provide a dressing mechanism for dressing the sides and tip of a grinding Wheel, in which the dressing tools will be moved back and forth across the surfaces to be dressed, and in which the rate of movement of the dressers in one direction will be faster than in the opposite direction, so as to provide first a rough-dressing operation and then a finish-dressing operation.

A still further object of the invention is to provide a dressing mechanism which can be adjusted readily for dressingr Wheels of various diameters, heights, pressure angles, and prole shapes.

Other objects of the invention will be apparent hereinafter from the specification and from the recital of the appended claims.

The dressing mechanism of the present invention in its preferred form is similar to prior types of dressing mechanisms in that it comprises three swinging arms, one of which carries a diamond for dressing the tip of the Wheel and the other two of which carry diamonds for dressing the outside and inside surta es of the wheel, respectively. The arms. which carry the inside and outside dressers, are actuated, as in prior types of dressing mechanisms, from a single fluid-pressure operated piston which is provided on opposite sides with racks that mesh with spur pinions that are secured to the dresser arms.

The arm, which carries the end dresser, is actuated by a second fluid-pressure operated piston through a rack, which is secured to that piston, and a pinion which is secured to the arm and which meshes with the rack.

The actuating piston for the side dresser arms is mounted in a block which, in turn, is angularly and rectilinearly adjustable on a swineable bracket. The angular adjustment is for positioning the side dressers in accordance with the desired pressure angles of the outside and inside surfaces of the wheel to be dressed. There are two rectilinear adjustments, one in the direction of the wheel axis and the other in a direction at right angles thereto. The rst serves to position the mean point of swing of the diamonds with relation to the heights of the active side surfaces of the wheel. The second is for the purpose of positioning the diamonds in accordance with the diameter of the wheel to be dressed. The swingable bracket is pivotally mounted on a slide which is adjustable rectilinearly on a ring-like support in a direction at right angles to the directions of the two previously described rectilinear adjustments, and is for the purpose ci positioning the dressing mechanism to dress selectively concave.

convex, or substantially straight line prolcs en the grinding wheel, in accordance with the principles 0f Wildhaber et al. Patent No. 2,311,302. issued February 16, 1943. The ring-like support is mounted coaxially with the grinding wheel axis and is adjustable about the axis in accordance with prior practice to permit positioning the dressing mechanism at a point around the grinding wheel remote from the point of engagement of the wheel with the werk. The pivotal movement of the bracket on the slide serves, however, to swing the dressers into or out of operative relation with the grinding wheel.

The end dresser arm and the piston, which actuates the same, are pivotally mounted on a slide for movement about an axis that extends at right angles to the axis of swing of this arm. The slide, in turn, is mounted on a bracket for adjustment rectilinearly in two directions at right angles t0 one another to position the end dresser in accordance with the diameter of the wheel to be dressed and in accordance with the height of the wheel. The bracket itself is adjustable angularly on the ring-like support above mentioned so that like the side-dressers the end dresser may be positioned at a convenient point about the periphery of the wheel to provide maximum clearance between the end dresser and the work.

The pivotal movement of the bracket, which carries the end dresser, serves two purposes, viz.,

to move the dresser into and out of operative position, and to control the shape produced on the tip surface of the grinding Wheel when the dresser is in operative position. In its latter function, the pivotal movement of the bracketv serves to swing the dresser, independently of its swinging movement from one side of the wheel to the other, and permits of dressing a plane surface on the tip of the wheel.

The pivotal movements of the brackets, which carry the side and end dressers into and out of operative relation with the wheel, are effected by separate pistons which are controlled from a single valve to operate simultaneously together. This control valve also governs the operation of the pistons which actuate the side and end dressers when the dressers are in operative position.

The control valve is moved step-by-step iirst in one direction and then in the other. During grinding of a. gear. the side and end dressers are out of operative position. When it is desired to dress the grinding wheel, the control valve is moved part-way in one direction to cause the side and end dresser brackets to be swung above their pivots to carry the side and end dressers into operative relation with the wheel. When this position is reached, the control valve is moved the rest of the way in this same direction causing the two pistons, which actuate the dressers, to be moved to effect rough-dressing of the sides, tip and rounds on the wheel by movement of the dressers in one direction across the grinding wheel. The control valve is then moved back one step in the opposite direction, causing the side and end dressers to swing back across the sides and tip of the wheel to eiiect nish dressing thereof. Then the operator moves the control valve back the second step to its original position, causing the side and end dresser brackets to be moved about their pivots to move the side and end dressers out of operative position to clear the work when the wheel is in use.

Check and throttle valves, which are incorporated in one side of the lines; of both the piston, which actuates the side dresser, and the piston, which actuates the end dresser, serve to control the rates of movement of each piston in one direction. so that the pistons may be operated at slower speed during their return movements from that during their forward movements. This permits of roughdressing on the forward movements and finish-dressing on the return movements. A reversible shuttle valve permits of the movement of the end dresser piston to be independent of the movement of the side dresser piston with the result that the end dresser may be moved at any desired rate with reference to the side dressers in both directions and may produce any desired iinish on the tip of the grinding wheel.

A lost motion device, comprising a ball and an inclined raceway for the ball, serves to shift the axial position of the arm which carries the outside dresser, .when the arm reverses at the ends of its swing. Thus, the arm may be displaced axially and the outside dresser may clear the wheel on its return stroke. Thus, the outside surface of the wheel may be rough-dressed only to avoid burning of the gear tooth surface which is ground by the outside of the wheel.

To produce feed of the wheel into the dressing tools to compensate for wheel wear, a ratchet and pawl mechanism is provided. This is actuated by a huid-pressure operated piston which is controlled from the same valve which controls the operation ofl the other parts of the dressing mechanism. The feed piston isactuated to advance-the wheel during swing of the side and end dressers into operative position.

In the drawings: l

Fig. 1 is an elevational view looking at the wheel end of a spiral bevel gear grinding machine of known construction and showing a dressing mechanism constructed according to one embodiment of the present invention mounted thereon;

Fig. 2 is part plan, part transverse sectional view of the parts shown in Fig. 1; V

Fig. 3 is a fragmentary view, partly in elevation and partly in. section, on an enlarged scale, showing the end dressing mechanism in operative relation to the grinding wheel; Y

i is a section on the line 4 5 of Fig. 3 on an enlarged scale, looking in the direction of the arrows; l

Fig. 5 is a view of the end dressing mechanism looking in the direction oi the arrow 5 in Fig. 3;

Fig. 6 is a fragmentary sectional view showing how the end dressing mechanism is mounted on supporting ring` which surrounds the grinding wheel spindle, and illustrating some of its adjustments;

Fig. 7 is a Jfragmentary view in plan showing the pivotal bracket for carrying the side dressing mechanism, its mounting, and the means for actuating the same;

Fig. 8 is an elevational View on a somewhat smaller scale of the parts shown in Fig. 7, portions being bro-ken awayV and shown insection:

Fig. 9 is a view, partly in section and partly in elevation, showing the mechanism for swinging the side-dresser bracket about its pivot'and its connection with the bracket;

Fig. l0 is a sectional view en an enlarged scale further illustrating the connection between the side dresser bracket and the piston which swings the bracket to and from operative position;

Figs. 11 and 12 are detail views, taken at right angles to one another, showing the lost-motion connection between the outside dresser arm and the cam which controls the aXial movement of that arm;

Fig. 13 is a sectional view of the shuttle valve which permits of operation of the end dressers independently of the side dressers;

Figs. 14 to 16 inclusive are diagrammatic views illustrating the operation of the valve which controls the operation of the whole dressing mechanism;

Fig. 17 is a developed view of this valve;

Fig. 18 is a diagrammatic View showing the hydraulic circuit to the various parts of the dressing mechanism;

Fig. 19 is a section on the line lS-IS of Fig. 18;

Figs. 20 and 21 are diagrammatic views illustrating the action of the side and end dressers in the successive steps of rough-dressing and nnish-dressing, respectively; i

Fig. 22 is a view corresponding to Fig. 21 but illustrating diagrammatically the operation when the outside dresser is in withdrawn position on its return stroke; and

Fig. 23 is a diagrammatic view illustrating particularly how the tilting movement of the end dresser during a part of its swing from one side of the wheel to the other serves to dress a iatv tip surface on the wheel.

Reference will now be had to the drawings for a more detailed description of the invention.

25 (Fig. 2) denotes the tool spindle of a grinding 7 machine off known construction. 2,5 is a sleeve member in which the tool spindle is journaled. W denotes a grinding wheel which is secured to the tool spindle by, for instance, a clamping disc 2 and a bolt 28. The wheel W is a rotary annular wheel having active outside and inside surfaces 3| and 32, respectively, which are inclined to the axis of the wheel, and a tip surface 33,

whichl ordinarily is perpendicular to said aXis.`

For clearness of illustration, the grinding wheel shown in Fig. 1 is somewhat smaller in diameter than the grinding wheel shown in Fig. 2.

There is a ring member 35 mounted on the flange portion 29 of sleeve 26 behind the grinding wheel. This ring member supports the dressing mechanism and is adapted to be adjusted on the sleeve 26 about the axis of the wheel to position the dressing mechanism at Whatever point may be most convenient to clear the work. It is secured in any adjusted position by a hand op- @rated spring-pressed plunger 35 which may be engaged selectively in one of several equi-spaced holes 31 that are formed in the periphery of the flange portion 29 of the sleeve 26.

The ring member 35 is formed with a lateral extension l0 on which is mounted a slide il (Figs. 1, 7, and 8). The slide 4| is adjustable rectilinearly on the extension 4i), and its adjustment is efectedby rotation of a screw shaft 42. This shaft is journaled in a plate 43 and threads into the slide 4|. The plate 43 is secured to the extension 45'by screws 54 (Fig. 2). The slide 4| is guided in its adjustment by a tongue 45 which engages in a T-slot 46 formed in the front face of the extension 40. An index pointer 41, which is secured to the slide 4| and Which reads against graduations enscribed on the face of the projectingportion 40, serves to permit of adjusting the slideprecisely. T-bolts (not shown), which engage iny the T-slot 46, serve to secure the slide to the ring S in any adjusted position.

Piyotally mounted on the slide 4| is a bracket 5i). This bracketis hinged to the slide by av hinge pin` 5.11 which is journaled in the slide 4| on bearings 52 and 53. The means for swinging the bracket 50 about the hinge pin 5| will be described hereinafter.

Mounted for rectilinear adjustment on the bracket 50 in` a-direction at right angles to the direction of adjustment of the slide 4| is a plate 55.v (Figs. 1 and 9). Adjustment of this plate may be` effected byY rotation of the screw shaft 56 which is journaled in the bracket 50 and which threads into a nut (not shown) that is secured to thepla-te 55. The plate 55 is guided in its adjustment by a tonguey 51 which engages in a T- slot 52; formed in the upper face of the bracket 591 A Vernier. 55, which is secured to the plate 55 (Fig. 1), and a scale 6U, which is secured to one side of the bracket 59, serve to permit precise adjustment of the plate 55 on the bracket. The plate is secured to the bracket after adjustment by T-bolts (not shown) which engage in the parallell T'-slots 58; and 52 (Fig. 9).

Mounted on the plate 55 for adjustment rectilinearly thereonv in a direction at right angles to the directions of adjustment of plate 55 and slide 4| is a plate 65. The plate 65 is guided in. its adjustment on the plate 55 by a tongue 65 (Fig. 1) which is integral with the plate 55 and which engages in a groove 5? formed. in the under face of the plate 65. Adjustment of the plate .65 on the plate 55 is effected by rotation of a screw shaftr 68 which is carried by the plate 65 and whichY threads into a nut (not shown) that is secured to the plate 55. This adjustment can be effected preciselyvby` use of the pointer 12 (Fig. 9) which is secured to the plate65 and which reads against graduations enscribed on one side of plate 55. The plate G5 is secured in any position of adjustment on the plate 55 by T-bolts 69 (Fig. 2) which pass through elongated slots 1) in the plate 55 and engage in T-slots 1| formed in the upper face of the plate 55.

Mounted on the plate 65 for angular adjustment thereon is a housing 15 (Figs. 1 and 2). Angular' adjustment of this housing is effected by rotation of a worm shaft 'I6 which is journaled in a block 1l that is doweled or otherwise fastened to the, plate 55. The worm shaft 'IS carries a worm 73 which mesheswith a worm wheel segment 18 that is fastened to the housing '15. The housing 15 is guided in its angular adjustment on the plate 65 by a tongue 'I9 which ls formed on the under face of the housing and which engages in a circular arcuate groove that is formed on the upper face of the plate 65. A flexible tongue 8i, which is integral with the block il and which is manipulated by the bolt 82 and which engages over an arcuate ange formed integral with thel housing 15, serves to clamp the housing in any adjusted position. A Vernier 84, that is integral withthe housing 15 and that reads against angular graduations provided on the upper face of the plate 65, serves to permit of adjusting the housing f5 precisely angularly on the plate 65.

Journaled on suitable anti-friction bearings .in the housing l5 are a pair of shafts 9? and Si (Fig. 2). These shafts are mounted in the housing so that their axes are inclined to one another at angle corresponding to the included angie between the inside and outside surfaces 3i and 32 of the grinding wheel which is to dressed. The shaft 9d carries an arm S2 in which is mounted the diamond 53 for dressing the outside surface 3i of the grinding wheel, The shaft 9| carries arm in which is mounted the diamond 5S for dressing the inside surface 32 of the grinding wheel, The arms 92 and Q5 are shaped in the conventional manner so that at a mean point of swing of the arm 95 the diamond 9S will engage the inside surface 32 of the wheel at a point lying in the same radial plane cf the wheel as the point of engagement of the diamond 53 with the outside surface of the wheel when the arm 92 is at a mean point of its swing. Further, the arms S2 and 95 are shaped and bent in the usual manner and the diamonds E? and Sii, respectively, are so mounted in these arms that each diamond will lie at substantially right angles to the side surface which it is to dress.

There is a spur gear segment 98 fastened to the shaft 95 and there is a spur gear segment 39 fastened to the shaft 9i: These segments mesh with racks i535 and lill, respectively. that are cut into opposite sides of a piston 4D?. The piston mi. is reciprocable in a cylinder |053 (Fig. i8) formed in the housing '55.

The end of the shaft Si', remote from that which carries the arm 92, is formed with an integral arm (Figs. 2. 1l and ISI). This arm carries a ball |65 which serves as :i follower to engage the face |61 of a cal U38 that secured in an end plate |69 which is fastened in suitable manner to the housing '55.

A coil spring H0, which surrounds n plunger Hi, serves to hold the ball-follower against the face |57 of the Cain. The plunger is mounted in a hole drilled in the shaft Sil and the spring H0 is interposed between the head H2 of the plunger and a nut which threads into the bore of the shaft 93. The plunger is secured in the housing by a nut I3 which threads onto the outer end of the plunger.

The ball |05 is mounted in a raceway ||5 (Fig. ll) whose internal diameter is somewhat larger than the diameter of the ball, and the ball is adapted to ride on the inclined surface H5 of a block ||l` which is mounted in the arm |55. The surface I ||5 is inclined in the direction of rotation of the shaft e@ so that when the shaft is reversed at the ends of its swing the ball ll may ride on the surface H6 to allow of axial movement ci the shaft. The ball and its mounting constitute, therefore, a lost motion device allowing axial movement of the shaft 95 for a purpose which will hereinafter appear in more detail.

The shaft Si has an arm H3 (Fig. 2) formed integral with it which is adapted to ride on the rear face of a cam |2|| that is secured to the housing i5. The arm i9 is held in engagement with the cam by a coil spring |2| which surrounds the plunger |22. Thisspring is interposed between the head of the plunger and thc shaft 9|.

The cams |58 and |23 control the prof-lle shapes dressed on the outside and inside surfaces, respectively, of the grinding wheel. The configurations of the active surfaces of these cams determine directly the profile shapes dressed on the wheel. Thus the active surface ital of cam |33 (Figs. l1 and 12) comprises a plane surface |23 perpendicular to the axis of the shaft 9|) and an inclined surface Hence, the cam |33 will cause the dressing tool 93 to dress a surface on the outside of the wheel of two different pressure angles in accordance with the principles of Stewart Patent No. 2,311,262. 1f it is desired to dress a straight proile of a single pressure angle from top to bottom, a plane surfaced disc is substituted for the cam |33 so that no axial motion, other than that produced by the lost motion device, is imparted to the shaft Si) during dressing.

From the structure described, it will be seen that when the piston HB2 is moved in one direction or the other in the housing 15, the arms Sil and 9| will be swung simultaneously in opposite directions to pass the dressing tools 33 and S6 across the outside and inside surfaces, respectively, of the grinding wheel and that during the swinging movements of the arms, am'al movements may also be imparted to them depending upon the shapes of the cams |63 and |23, and also, in the case of the shaft 33, upon the lost motion device ISG-I i8. Thus by use of suitable cams |33 and |25 any desired shapes can be dressed on the outside and inside surfaces of the grinding wheel, and through the lost motion device, the outside dressing diamond can be moved clear of the outside surface of the wheel on the return stroke of the arm 92 so as to dress on` movement `of this arm in one direction only.

As has already been stated, bracket 5t is pivotally mounted upon the slide di (Figs. 7 and). The pivotal movement of the bracket is for the purpose of swinging the side dressers into and out of operative engagement with the grinding wheel. The pivotal movement of the bracket is produced by a piston |25 (Figs. 9 and 18) which is mounted to reciprocate in a cylinder |25. One end ofv this cylinder is closed by an end cap |21 (Figs. 9 and 10) which is secured by screws (not shown) to the cylinder. This end cap is releasably secured to the bracket 55 by means of a keeper |23 which engages a headed pin |23 that is secured by a pressed t or otherwise in the bracket. The keeper |28 is pivotally connected to the end cap |21 by means of the hinge pin |35`v and it is secured in engagement with the pin |29 by the hinge bolt 3| and the nut |32. hinge bolt |3| is pivoted on the cover plate |21 by means of the pin |33, and the nut |32 threads Onto the hinge bolt |31 to hold the keeper |28 in engagement with pin |29- The piston |25 is xed against movement relative to the slide It has a rod portion |35 which projects through the end cap |35 of the cylinder |25 and which threads into a block |31 that is pivotally mounted on a pin |38. The pin |38 is secured in the slide il against movement relative thereto by a set screw |39.

Ducts 1de and itl are provided in the end plate |21 and the side wall of the cylinder |23, respectively, for admitting fluid under pressure to opposite ends of the piston |25. When the line |43 is on pressure, the bracket 53 will be swung about the hinge pin 5| (Figs. 7 and 8) to move the side-dressing mechanism out of operative re- 'lation with the grinding wheel, and when the duct is on pressure, the side dressing mechanism will be returned again into operative relation with the wheel.

The tip surface of the wheel is dressed by a diamond |65 (Figs. l and 2) which is secured in an arm Md that has a split-clamp connection with a shaft H51 (Fig. 3) and that is held against axial movement relative to this shaft by means of the washer |48. This washer is secured to the shaft by a screw M9. The shaft |41 is journaled on suitable bearings |5|l and |5| in the housing |52. This housing is bored to provide a cylinder |53 (Figs. 4 and 18) in which there is reciprocably mounted a piston |54. The piston |515 is provided at one side with rack teeth |55 that mesh with the teeth of the spur pinion |56 which is keyed to the shaft |41. Thus, as the piston |54 is reciprocated in the cylinder |53, the shaft M1 is rocked in one direction or the other to move the diamond M5 across the tip of the grinding wheel from one side thereof -to the other to dress the tip of the wheel and rounds at the junctures of the tip with the sides of the wheel.

The housing |52 is mounted to swivel on a slide |53 for movement about an axis which extends in a direction perpendicular to the axis of oscillation of the shaft |111. For this purpose, there is a swivel stud I5! secured in the slide |69 by a nut |E2 which threads onto the lower end of the stud. The housing |52 is mounted on the stud |5| yby a circular collar |63 which engagesA under the enlarged head portion |65 of the stud and which is secured to the housing |52 by the screws |66. A spacing washer |61 is interposed between the coilar |53 and the vhousing |52.

The housing |52 may be oscillated about the axis of the centering member |5| for two purposes, namely, to produce a substantially fiat tip surface on the grinding wheel as the end dresser |45 swings from one side to the other of the wheel, and t0 move the end dresser HB5 out of or into operative relation with the wheel. The first movement is accomplished by means of a cam |1|| (Figs. 3 and 5) which engages with a rider or follower |1. The cam is mounted for rotatable adjustment on a disc |13 that iskeyed to the shaft |41. The rider or follower |1| is in the form of a pin which is threaded into an upright arm |12, that is integral with the slide |65. The follower has a conical inner end that engages the peripheral surface of the cam lli). The cam is secured against rotation relative to the disc |73 by a nut |35 and washer |16. The nut |15 threads on the shaft |51. The adjustment of the cam on the disc permits of controlling the angle of inclination to the axis of the grinding wheel of the tip surface dressed on the wheel. By adjusting the cam angularly about the axis of shaft |51, the point, at which the housing |52 is rocked by the cam, can be adjusted, so that the plane tip surface dressed on the wheel can be made perpendicular to the axis of the wheel or can be inclined thereto at any suitable angle. Ordinarily the tip of the wheel is dressed to be perpendicular to a line bisecting the angle between opposite sides of the wheel. Adjustment of the cam on disc |13 can be made precisely by use of the pointer lii (Fig. l) which reads against suitable graduations provided on the `periphery of the cam.

The swivel movement of the housing |52 for movement of the enddresser to and from operative .position is eifected by reciprocation of a piston :|30 (Figs and 18) that is reciprocable in a cylinder |8| `which is vintegral `with the slide |50. The piston |85 is formed .with a rod portion |82 which projects through the end plate |03 of the cylinder 58| and which has a threaded and split clamp connection with a coupling piece |84. lThis coupling piece |84 "has a pivot'ed connection at |85 with a piece |86 into which is threaded a plunger |81. The plunger |81' extends into a sleeve |58 which is pivotally connected by means of the pin |85 (Figs. 3 and 4) with the housing |52. The pin |89 threads into the housing |52. There is a coil spring |55 that surrounds the plunger |87 and that is interposed between the head of the plunger and a cap |9| which threads into the open end of the sleeve |88. The spring tends to hold the end dresser in operative position in combination with the pressure on the right hand end of the piston |80 (Fig. 3). When pressure is applied to the left hand end of the piston Sil, however, the end-dressing mechanism is swung about the pivot stud |6| so that it is moved away from operative relation with the grinding wheel.

The slide |55 has a dove-tailed portion 250 which engages in a correspondingly shaped groove 20| in the bracket |25, and is mounted for rectilinear adjustment on a bracket |55 (Figs. 3, 5, and 6). A gib 202 serves to take up wear. The adjustment of the slide is effected by rotation of a screw shaft |56 which is journaled in the bracket |95 and 'which threads into a nut (not shown) that is secured in the slide. A tubular guard |57, that is secured to the slide, serves to protect the threaded portion cf this shaft from dirt and grit. The adjustment of slide |60 on the bracket |25 is provided to permit of proper positioning of the end dresser in accordance with the diameter of the grinding wheel to be dressed. This adjustment can be made precisely through use of the Vernier |98 which is secured to the slide E50 and which reads against a graduated scale |99 that is fastened to the bracket |95.

The bracket |95 is adjustable rectilinearly on a plate 205. This adjustment, which is in a, direction at right angles to the direction of adjust` ment of the slide |60 on the bracket |95y is for the purpose of positioning the end dresser in accordance with the height of the grinding wheel, that is, in accordance with the axial position of the tip surface of the wheel. It may be effected manually under control of a Vernier 206 which is secured to the plate 205 and which reads against a scale 251 that is fastened to the bracket |95. After the adjustment is made,the bracket v|55'is fastened to the plate 205 by means of the bolt 208 that threads into a Anut 209 which engages in a slot 2|0 formed in the upper face of the plate 205. The bolt 208 is mounted in the thimble 2| which is flanged to engage the bracket |95. A lock-nut 2|2 serves to hold the bolt securely after the adjustment is made.

The .plate v205 is mounted on the ringimember 35 for adjustment around the periphery -of the ring member about the axis 'of the wheel spindle. This adjustment permits of positioning the end dresser at any convenientl point around the periphery of the grinding Wheel so as to minimize the possibility of interference between the enddressing mechanism and the work even in withdrawn position of the end-dressing mechanism. The plate 225 is secured iii-any adjusted position on the ring member T35 by two T-shaped tongues 2|5 (Figs. 3 and 6) 'which engage in a T-shaped groove 2|5 formed `on the periphery of the ring 35 and which serve to guide 'the plate 205 in vits adjustment on Vthe ring. Bolts 2H, which are carried by plate 205, serve to move the tongues 2 t5 intoand-outof clamping position.

The operation of the dressingmechanism shown in the dra-wings is controlled by a manually rotatable valve 220 (Figs. 17 and 18) which is journaled in the sleeve 22| 'that 'is mounted in the bracket 222. The bracket 222 is secured in any suitable position on the grinding machine. The valve 223 is rotated by Ia -lever 223 which is secured in a head 224 that is pinned to the stern portion 225of the valve 220. 'The stem portion 225 of the 'valve projects outwardly through the plates 226 that-close-one end of the casing 222. The opposite end ef the casingr is closed by a plate 221.

Thevalve is 'formed-on Vits `periphery with two elongated grooves-230 and with two pairs of shorter-grooves 23| and`252. All of these grooves extend axially of the valve. The grooves 230 are connected, however, by a groove 233 which extends aroundthe periphery of the valve.

The sleeve 22| (Figs. 14, 15, 16 and 18) is provided with seven peripheral grooves 235 to 24| inclusive which are equi-spaced axially of the sleeve. Radial ports, which are drilled in the sleeve V2.5, communicate with each of these grooves. Thus, there are four ports 245, communicating with Vgroove 235; there are four ports 255, communicating with groove 236; two ports 251, communicating with groove `231; four ports 248, communicating Ywith groove 238; 'four ports 249, communicating with groove 239; two ports 25o, communicating with groove 240; and four ports 25|, communicating with'groove 24|. The different ports of each group Aare spaced angularly from one another about the axis of the sleeve 22| and valve 220 as best shown in the developed'views of Figs. 14 to 16 inclusive. The shoulders formed on theisle'eve '22| between the several grooves 235 to '24| inclusive separate the different groups of ports from one another so that the motive iiuid may'fiow from one group of ports to another only through the grooves 235, 23|, 232, and 233 of the valve`22.

The pressure uid is supplied to the valve 220 from ducts 255 and 25| (Fig. 18). The duct 250 is connected with any suitable source of uid supply. The duct 25| communicates with the groove 238 and ports 2&8 in sleeve 22|. The motive fluid is exhausted from the valve 225 through the ducts 252 and 253. The duct 252 communicates With 13 the valve through the groove 24| and ports 25| of sleeve 22 l, and the duct 253 communicates with the valve through the groove 235 and ports 245 of sleeve 22|.

The groove 239 and ports 246 in the sleeve 22| communicate with a duct 255. This duct is connected by means of a duct 255 and a duct 251 with one end of the cylinder I 8| in which the piston |99 reciprocates that moves the end-dressing mechanism to and from operative position. The duct 255 is also Connected by means of the duct 255 and duct |49 with one end of the cyl inder |26 in which the piston |25 reciprocates that moves the side-dressing mechanism to and from operative position. The connection between the duct |49 and the cylinder |26 is controlledby two ball check valves 259 and 259. The ball check valve 253 is normally constrained by a coil spring 252 to prevent ow of the motive fluid from the duct |99 into the duct 259 whence it may ilow into the cylinder |26. The ball check valve 259 is normally constrained by the coil spring 293 to prevent flow of the motive fluid from the cylinder |29 through the ducts 299 and 25| into the duct Idil.

The duct 255 is also connected with one end of a cylinder 255 in which a piston 285 is reciprocably mounted. The piston 255 is intended to operate the mechanism for feeding the grinding wheel into the dressers to determine the amount of stock to .be removed from the wheel and to compensate for wear of the wheel. .The piston 299 may be connected to the feed mechanism of the grinding machine in any suitable manner to operate same. As shown, it is connected by the piston rod 261 and a link 268 with one arm of an oscillatable member 259 that is mounted to pivot about an axis 219. Pivotally mounted on another arm of the member 269 is a pawl 21| which is adapted to engage a ratchet ,wheel 212 that is mounted to rotate about the axis 219. This ratchet wheel may be connected, for instance, to a feed screw that imparts feed movement to the grinding wheel so that on each reciprocation of the piston 259 a step-by-step feed movement may be imparted to the wheel to feed the Wheel into the dressers.

The groove-23'! and ports 221 in the sleeve 22| communicate with a vduct 215 which is connected to one end of the cylinder ISI in which the piston |89 reciprocates. This duct 215 is also connected with one end f the cylinder |25 by the duct HH, and it is connected with one end of the cylinder 255 b-y the duct 216.

The groove 299 and ports 250 in the sleeve 22S communicate at opposite sides of the sleeve 22| with ducts 395 and 951 (Fig. 19). A ball check valve 399 is normally pressed by a coil spring 399 into position to close off communication between the duct 391 and a duct 289. A needle valve Sie, which threads into .the valve casing 222, serves t0 control the opening between the duct 289 and the duct 395. The duct 289 leads to one end of the cylinder |93 in which the piston |02, that actuates the side dressers, reciprocates. The opposite end of the cylinder is connected by the duct 29 I with the groove 239 and ports 229 in the sleeve 22|.

The duct 29| also communicates with the cylinder IIJ-3 either through the duct 292 or the duct 293. Both of these ducts connect with a duct 282 which leads to the lower end of cylinder |93. The connection betweenl the duct 282 and the duct 28| is controlled byneedle valve 285 which is adiustablv threaded mwa-Cep member 286 that is secured in any suitable manner .to the housing 15 and that serves to close one end of cylinder |03.'

Communication between the duct `28| and the duct 293 is normally closed by a ball check valve 281 under actuation of the spring 288.

The duct 28| is also connected by a duct 290 with one end of a chamber o-r casing 29| (Figs. i3 and 18) which houses the sleeve 292 and the valve 293 that reciprocates therein. The valve 293 is normally urged in one direction by a coil spring 294 which is housed in a bore in the Valve` and which is interposed between the inner end of this bore and the cap member 295 which closes one end of the valve chamber. The duct 299 is threaded into the cap member 295 which closes the other end of the valve chamber. The sleeve 292 is formed with ve groups of radial ports. These ports are denoted at 291, 299, 299, 399 and 99|, respectively. The valve 293 is formed with three axially spaced partition shoulders 303, 39d

and SI15.

The valve 293 is a shuttle valve and serves in the embodiment of the invention illustrated in the drawings to permit of movement of the end dresser independently of the side dressers. The pressure fluid is supplied to the valve -293 from the line 259 through the duct 3|9 which communicates with the ports 299 in the sleeve 292. The motive fluid is exhaustedv from the valve cham-ber 295 either through the duct 3| I, which communicates with the ports 291 in sleeve 292, or the duct 3I2, which communicates with the ports 39|. The two ducts 3I| and SI2 are connected to a duct. 953 which leads to the sump of the grinding machine.

The valve chamber 29| is connected to one end of the cylinder i153, in which the piston |54 reciprocates, by a duct 3|5 which communicates'withY the ports 298 in the sleeve 292. The valve chamber 29| is connected to the opposite end of the cylinder i5@ through a duct 3| 9 which communicates with the ports 399 in the sleeve 292. The duct 9i E connects with the mentioned end of the cylinder |53 either through a duct SI1 or a duct 38. Communication between the duct 3| 6 and the duct 3|1 is controlled by a normally closed ball-check valve SIG that is urged into closed positionby a coil spring 929.- Communication between the duct SIB and the duct SIS is controlled by a needle-valve 92d which threads into the cap member |51 that closes one end of the cylin4 der |53.

The parts are shown in Fig. 18 in the positions which they occupy when the side and end-dressing mechanisms are out oi operative position. This corresponds to the position of the valve 229 which is diagrammatically illustrated in Fig. 14. In this figure and' in Figs. 15 and 16 the grooves in the valve body are shown in dotted lines opposite the ports of the valve sleeve 22| with which the grooves are in communication at differentl steps in the rotary movement of the valve. Figs. i4, l5 and 16 represent successive positions of the valve as it is rotated in the sleeve. l

In the position of the valve shown in Figs. 14 and 18, the pressure fiuid flows from the ducts 259 and 25| through the ports 229, grooves 239 and 293, and ports 295 and 299 int-o the ducts 255 and 29|. At the same time, the duct 2,15 is on exhaust through the ports 241, grooves 232, and ports 245, while the duct 289 is on exhaust through Jthe needle valve 3M (Fig. 19) duct 396, ports 259 in the sleeve 22|, grooves23| in the valve body 229, and ports 25| in the valve sleeve The pressure fluid fiowing into the .duct '255 holds the piston |80 'to the left in the position shown in Fig. 18, holding the end-dressing mechanism in inoperative position. The pressure uid owing through the duct 255 also `holds the piston 286, which controls the feed of the grinding wheel, at the right end of the cylinder 285 with the'pawl 21| in reset position. The pressure-fluid also 'flowing through the duct 255 into the ducts 256 and'l40 forces the ball-check valve v258 open against the resistance of the'spring 262, but closes `th'eball-check valve 259. Thus it flows into the cylinder ll`2'6'th'roug'h the lduct 250 to hold the piston 'at the right hand position shown in Fig. 18, holding the side-dressing mechanism in 'inoperative position.

-In the described position of valve 220, the pistons |02 and |54, which operate the side and end dressers, respectively, remain at 'the upper ends oftheir cylinders |53 and |53, respectively,in 'the positions shown in Fig. 18, for the pressure fluid flowing through the line 28| enters the lower end of the cylinder |03 throughthe open ball-check valve'281 and the ducts 283 and 284, while the shuttle valve 293 isheld in its lowermost position in the valve chamber 29| through flow of the pressure uid 'from the ducts 28| and 290 into the upper end of the valve vchamber 29|. With the valve 293 in its lowermost position, the pressureuid iiows from the duct 3|0, through the ports 299 and v298 of sleeve 292 into the duct 3|'5 to the-'lower end of the cylinder |53, while the upper end of this 'cylinder is on exhaust through the duct 3|8, throttle valve |51, duct SI5, ports 300 and 30| of sleeve 292, and ducts '3|2 and 3|3.

When the operator wishes to eect dressing of the grinding wheel, he rotates the valve 220 by the Vhandle 223 to move the valve to the rst position indicated diagrammatically in Fig. 15. This reverses the direction of ow of the motive fluid through the lines 255 and 215, while maintaining the'previous direction of flow of the motive fluid through the lines 28| and 280. Thus the line 215 is put on supply through the ports 248, grooves 230 and 233, and ports 2131, while the line 255 is put on exhaust through theports 248, grooves 232, and ports 2115.

With the line 215 on supply and the line 255 on exhaust, the pressure-fluid forces the piston |80 to the 'right in the cylinder |8| lfrom the position 'shown in Fig. 18, the right 'han'd end of the cylinder |8| exhausting through the lines 251, 256 and 255. Thus, the end-dressing mechanism is swung into operative position 'through the connection of the piston-rod |82 (Figs. 3 and 4) with the housing |52 which carries the-enddressing mechanism. With the line 215 on supply `and the line 255 on exhaust, the piston |25 is also 'forced to the left in the cylinder |26 from the position shown in Fig. 18, thus causing the side-dressing mechanism to be swung also about the hinge 5| (Figs. 7 and 8) into operative position through the connection of the piston-rod with the slide 4| (Fig. 9) which supports the side-dressing mechanism. At this time 'the exhaust fluid flows from the left-hand end of the cylinder |26 through the duct 290, the vnow-open ball-check valve 259, and the lines |40' and 256 into line 255.

With the line 215 on supply and the line 255 on exhaust, the piston 268 is also actuated, being shifted to the left from the position shown in Fig, 18. This causes the pawl 21| to rotate the ratchet'wheel 213 actuating the wheel-feed mechanism of the grinding machine, thereby feeding 1'6 the grinding wheel into the Adressers in accordance with .the amount of stock which it is Vdesired to dress off the wheel inthe subsequent `dressing operation.

During the described movements of the side and end-dressing mechanisms into operative position and feed of the grinding wheel, the pistons |02 and |54, which roperate the side and end dressers, respectively, remain at the upper ends of their cylinders |03-and |53 in the positions shown in Fig.18, forthe line 28| remains on 'supply'andlthe line 280remains on exhaust.

`With the side and end dressers in operative position,-the operator rotates the valve220- still further to the position vshown diagrammatically in Fig. 16. This puts the lin'e 280 on supply through the ports 248, grooves 230fandf233, ports 250, and ducts 305 and -301 (Fig. 1`9), while the line`28| is put on exhaust through the ports 239,-grooves 231| and ports 2`5l. At the same time, the line 215 remains on supply and the -line 255 on exhaust, thus 'keeping the dressing mechanisms in their operative positions.

With the line 200 'on supply, the pressure-fluid flows into the upper end of the cylinder |03 forcing the vpiston |02 downwardly in the cylinder |03 from the position shown in Fig. 18, causing the side dresser arms 92 and 95 to be'swung in one direction to rough-dress the outside and inside surfaces Aof the grinding wheel. At this time, the lower-end of 'the cylinder |03 is on e'xhaust through the duct 284 and needle-valve 285.

With the line 28| on exhaust, the line 290 Ais also on exhaust. Hence, the Yspring `294 forces the shuttle valve 293 upwardly in the valve chamber 28| vfrom the position shown in Fig. 18. Thus the line 3|'6 is put on supply from the line 3|`0 through the -por'ts 299 and '300 of sleeve I292 (Fig. 13), and the line 3|5 is put on exhaust through the 'ports 298 and I'2910i sleeve i292, and lines 3|| and 3| 3. Thus, the piston |54 is forced downwardly in `the cylinder |53, causing the end dresser lto swing in one direction about the axis of its shaft I '41 -(Fig. 3) to effect rough-dressing of the tip of 'the' grinding wheel.

It will be noted that the rough-dressing movement of the end-dresser is unthrottled, and hence the end-dresser 'sweeps over the rounds and tip of the wheel at the rapid rate induced vby full pressure of the motive nuid -on the piston |54. The rough-dressing movement of the side dressers may `be limited, however, by the setting of the lthrottle valve 285. The relative rates of the rough-dressing movements of side and'end dressers may, therefore, be adjusted as desired.

'Theoperator now reverses the direction of rotation of the valve 220, moving the valve back 'from the position shown diagrammatically in Fig. 16 to that shown diagrammatically in Fig. 15. This again places the line 28| on supply and the line 280 "on exhaust'while maintaining the lines 215 and 255 on supply and exhaust, respectively. With the line 28| on supply, the motive fluid flows through the ball-check valve 281 and ducts 282, 288, 283, and 284 to the lower end of the cylinder |03 forcing the piston |02 upwardly in the cylinder to the position shown in Fig. 18, causing the side dressers to be swung back across the 'grinding wheel. During this return movement, lthe motive uidexhausting from the upper end of the cylinder |03 through the duct 282 is Vthrottled by the throttle valve 3|4, for at this stage the ball-check valve 308 is closed by operation of the spring 309 and by the pressure of the fexhaust iluid on the "ball, Thus,'the rate of the return or finish-dressing movement of the side dressers is controlled by the setting of the throttle valve 3M.

With the line 28| on supply, the line 290 is put on suuply also, causing the valve 293 to be forced downwardly in the valve chamber 29|, putting the line 3|5 again on supply from the line 3|0 and putting the line 3|6 again on exhaust through the line 3|2. This causes the piston |54 to be forced upwardly in the cylinder |53 back to the position shown in Fig. 18, causing the end-dressing diamond U to be swung in its return or finish-dressing movement across the tip of the grinding wheel. In this return movement, the upper end of the cylinder |53 is on exhaust through the duct 3|8 and the throttle valve 32|, for the spring 3|1 and the pressure of the exhaust fluid close the ball-check valve 3|9. Thus, the rate of the return or finish-dressing movement of the end dresser may be controlled by the setting of the throttle valve 32|. It will be noted, therefore, that the throttle valves 3M and 32| permit of adjusting separately the rates of finishdressing movements of the side and end dressers.

The operator now rotates the valve 220 back on to the position shown in Fig. 14. This keeps the lines 28| and 280 on exhaust and supply, respectively, holding the pistons |02 and |54 in starting positions, but it puts the line 255 on supply and the line 21-5 on exhaust. This causes the piston |80 to be moved back. to the left and the pistons and 256 to be moved back to the right to the positions shown in Fig. 18. The piston |80 is moved back to the left by flow ofthe pressureuid from the line 255 through the ducts 256 and 251, the motive fluid exhausting from the left hand end of cylinder |8| through the duct 215. Thus, the end-dressing mechanism is swung to inoperative position about the axis of the stud 16| (Fig. 4) through the connection between the piston rod |82 and the housing |52. The piston |25 is moved back to the right by flow of the pressureiiuid from the line 255 through the lines 2-56 and |40, the ball-check valve 253, and duct 260 into the left hand end of the cylinder |26. Thus, the side-dressing mechanism is swung to inoperative position through the connection between the piston rod |35 and the slide 4|, which carries the side-dressing mechanism (Figs. 9, 7, 8, and 1). At this time, the right hand end of the cylinder |25 exhausts through the duct |4| and line 215. The piston 266 is moved back to the right by ilow of the pressure-duid through the line 255, the right-hand end of the cylinder 265 exhausting through the lines 216 and 215. This causes the pawl 21| to be reset with reference to the ratchet feed mechanism.

In the forward or rought-dressing strokes of the side and end dressers, the tip of the outsidedressing diamond moves in a plane 340 from a position such as denoted in dotted lines at 93 in Fig. 20 to the position 93", while the insidedressing diamond moves in a plane 34| from a position such as denoted at 96 this gure to the position 96", and while the end-dressing diamond moves in an arcuate path from a position such as denoted at |95 to the position |95. During the movements of the dressing diamonds, the grinding wheel is, of course, rotating on its axis at high speed.

In prior types of dressing mechanisms, the three dressers were Connected to operate together and to complete their operation together. As will inside dressers have to cover in the dressing operation is much greater than the distance which the end dresser has to cover. As a result, in prior dressing mechanisms, the end dresser traveled at a much slower rate around the tip of the wheel than the rate of travel of the side dressers across the side surfaces of the wheel. Consequently in prior dressing mechanisms the end dresser dressed a helical surface of much finer lead on the tip surface of the wheel than the helical surfaces dressed bythe side dressers on the side surfaces of the wheel. The tip surfaces became, infact, practically burnishing surfaces and this is what caused burning of the bottoms and fillet portions of the tooth spaces of gears when the sides and bottoms of the tooth spaces were ground simultaneously.

This defect has been overcome with the present invention by provision of means for independenth1 adjusting the rates of movement of the side and end dressers. During rough-dressing, the exhaust line 3 5 from the end dresser may be full open and the end dresser may travel at top speed over the rounds and tip of the wheel. By properly adjusting the valve 285 (Fig. 18) then, the rate of travel of the side dressers can be adjusted to roughdress outside and inside helical surfaces on the whe-el whose pitch or lead P is equal to or but slightly different from the pitch or lead P of the helical surfaces rough-dressed on the tip and rounds of the wheel.

The lead of the finished surfaces dressed on the sides of the wheel is controlled in the dressing mechanism illustrated, as already stated, by the setting of the throttle valve 3M, and the lead of the finished tip surface of the wheel is controlled by the setting of the throttle valve 32 l. The shuttle valve 293 makes the movement of the end dresser independent of the movement of the side dressers and. moreover, insures that sufcient pressure is applied to the two pistons |02 and |54 to operate both in the time interval desired; the pressure line 3|@ that leads to the shuttle valve 293 is independent of and does not bleed the pressure line 255i that leads to the control valve 220. By adjusting the throttle valves 3 I4 and 32 I, then, a helical surface can be dressed on the tip of the wheel which is of approximately the same lead as the helical surfaces dressed on the sides of the wheel. This is illustrated diagrammatically in Fig. 21, where it will be seen that the pitch P of the finish-dressed tip surface of the wheel is equal to the pitch P of the finish-dressed side surfaces of the wheel. In Fig. 2l, 96'" denotes the position of the insidel dressing tool at the end of its return or iinishing stroke, while 93' denotes the position of the outside dressing tool at the end of its return or finishing stroke, and |95'" denotes the position of the tip-dressing tool at the end of its return or nish stroke. In the iinishing strokes, these toois move from the positions shown at 66", S3", and |95, respectively, in Fig. 20 to the positions denoted at 96', 93', and

|Q5'", respectively, in Fig. 21.

In the diagrammatic View of Fig. 21, it is assumed that the outside dresser is in Contact with Vthe wheel during its return swinging movement.

This would be the case if there were a rigid or non-slipping contact between the arm |05 (Figs. .l1 and 12) and the cam or disc |08 which controls the axial position of the shaft that carries the outside dresser. Where the arm |05 is con.. nected, however, to the control cam |08 through a lost Y'motion device, such as the ball |06 and taper block I1 shown in Fig. 11, then on reversal of the motion of the shaft 90 at the end of the forward or roughing stroke of the outside dresser, there will be a slippage of the ball en the cam surface with the result that the shaft 90 will be axially displace rearwardly and the outside dresser will clear the outside surface of the wheel on the return or nishing stroke of the dresser. Hence. the outside surface ofthe wheel will not be dressed on the return stroke, but will have the finish produced on the roughing or forward stroke only of the outside dresser. A wheel so dressed is illustrated diagrammatically in Fig. 22 where 34Go denotes the plane of swing of the tip of the outside dresser on its return stroke and 93a denotes the position of the outside dresser at the end of its return stroke. The inside dresser and tip dresser will perform the finish dressing operations on the inside and tip surfaces of the wheel as before. Thus, the inside and tip surfaces of the wheel will be dressed to helices having pitch P whilethe outside surface will be left dressed to a helical surface having the pitch P. A A wheel such as shown in Fig. 22 can be used to grind gears at much higher speeds without fear of burning than can be done with any prior type wheel. Moreover, the gears will have substantially the same surface finish on both sides and in the bottoms of the tooth spaces.

If a circular disc, instead of a cam |10, is mounted on the shaft |41 (Fig. 3) to engage the follower Ill, then the only movement that the rend dresser has during dressing is a simple swinging movement about the axis of the shaft |41, and the end dresser will dress an arcuate tip surface on the wheel as shown in Figs. 20 to 22 inclusive. By employing a suitable cam |16, ,howevery the end dresser can be rocked about the axis of the stud ISE (Fig. 1) during swing of the shaft |41 so as to dress a substantially fiat surface on the Wheel. This is illustrated diagrammatically in Fig. 23. Here Sail and 343| again denote the planes of movement of the outside and inside dressers S3 and S6. During the rst part of the swing of the end dresser from one side of the wheel to the other, a dwell portion of the cam VFD' is in contact with the rider, VH, and the movement of the dresser is effected solely by the rotationof the shaft |41 on its axis. Hence, the dresser may move from the position |951 to |552 dressing around at the juncture of the tip surface 33 of. the wheel with the outside surface 3|. Then the riseon the cam surface lli] comes into engagement with the rider VH and causes the whole end-dressing mechanism to be swung about the axis of the shaft |5| as the shaft Ili! continues toA rotate. The swinging movement about the stud |G| causes the dresser to dress a substantially fiat surface on the tip of the wheel. In this movement, the diamond travels from position |952 to |953. Then the rider Il! again rides on a dwell portion of the cam |15 and the movement Aof the diamond is again controlled wholly by the swing of the shaft IM. Hence, as the dresser moves from position I 953 to position |954, it dresses a round at the juncture of the inside surface 32 of the wheel with the tip surface 33 thereof. Of course, in the movements of the dressers they turn up helices on the surfaces being dressed, as already described, but these helices have been omitted in Fig. 23 for the purpose of clearness in illustration.

The, operation of the dressing mechanism of the present invention, as illustrated, will be understood from the preceding description but may be summed up hereV briefly. First of all, of course, the various adjustments are made that are. required to position the dressers in correct dressing relation to the wheel. Thus, the ring member 35 (Figs. 1 and 2) is adjusted on sleeve 29 to position the side dressers at a point to minimize possibility of interference of the side-dressing mechanism with the work during grinding, and the plate 285 (Fig. 5) is adjusted on the ring member 35 to minimize possibility of interference of the end-dressing mechanism with the work; the slide dl is adjusted rectilinearly on the extension 5B (Fig. 8) of the ring member 35 in accordance with the principles of Wildhaber et al. Patent No. 2,311,302 above mentioned and depending on whether substantially straight, convex, or concave profiles are desired on the sides ofy theV grinding wheel; the plate 55 is adjusted rectilinearly on the bracket 50 (Figs. 1 and 9)"in accordance with the diameter of the grinding wheel to be dressed; and the plate 65 is adjusted rectilinearly on`the plate 55 in accordance with the height of the wheel; the housing '.'5 is ad# justed angularly on the plate 55 in accordance with the pressure angles of the inside and outside surfaces of the wheel. Thus, also, the bracket is adjusted on the plate 255 (Fig. 5) to position the end dresser in accordance with the'height of the wheel; and the slide |68 is adjusted on the bracket |55 in accordance with the diameter of the wheel. The throttle valve 285 (Fig. 18) is adjusted to control the rate of movement of the side dressers relative to that of the end dresser during rough-dressing; and the throttle valves 3M and 32| (Figs. 19 and 18) are adjusted to control the relative rates of movement of the side and end dressers during finishdressing. Cams |19', |58 and |29 (Figs. 3, 5, 11, 12, and 2) of suitable configuration are selected in accordance with the shapes which it is desired to dress on the tip and sides of the wheel.

Assuming that the necessary adjustments have been made, when the operato-r desires to dress the wheel, he moves the control valve 229 from the position shown in Fig. 14 to that shown in Fig. 15 to put the line 215 on supply and the line 255 on exhaust and bring the side and end dressers into operative position and advance the grinding wheel axially in accordance with Wear of the wheel and the amount of stock to be removed therefrom. Thus, the piston |88 swings the housing |52 (Figs. 3 and 4) about the pivot stud |21, moving the end dresser into operative relation with the grinding wheel; the piston |25 swings the bracket 5U (Figs. 7, 8 and 9) about the hinge pin 5| moving the side dressers into operative relation with the grinding wheel; and the piston 266 (Fig. 13) rocks the arm 269 causing the pawl 21| and ratchet wheel 213 to actuate the wheel-feed mechanism.

Then the operator moves the control valve 220 (Fig. 18) on further to the position shown in Fig. 16to put the line Z853 on supply and the line 28| onexhaust. This forces the piston |22 downwardly to rock the side-dresser arms 92 and 95 (Figs. l and 2) about the axes of shafts 90 and 5 l; respectively, causing the side dressers to roughdress the outside and inside surfaces of the wheel; and it permits the spring 29.4 to shift the shuttle 'valve 233, putting the line :HGV on supply and the line 315 on exhaust, causing the piston |54 to swing the arm |66 (Figs. 3 and 4) and move the end dresser over the tip of the wheel from one side thereof to the other to rough-dress the tip of the wheel and the rounds joining the tip with the sides of the wheel. During the described rough-dressing movement of piston IU?, the rate 

